It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine valves, especially the intake valves, under certain engine load conditions. A known approach to providing selective deactivation is to equip the hydraulic lifters for those valves with means whereby the lifters may be rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated pushrods. Typically, a deactivation lifter includes, in addition to the conventional hydraulic lash adjuster, concentric inner and outer portions (pin housing and lifter body) which are mechanically responsive to the pushrod and to the cam lobe, respectively, and which may be selectively latched and unlatched to each other, typically by the engagement of pressurized engine oil acting upon one or more spring loaded latching pins extendable from the pin housing into recesses in the lifter body. See, for example, U.S. Pat. Nos. 6,497,207 and 6,814,040, the relevant disclosures of which are incorporated herein by reference.
In prior art deactivating hydraulic valve lifters, when the movement of the locking mechanism is incomplete at the start of a valve lift event, the lifter may start to open the engine valve and then allow it to close rapidly as the partially-engaged locking mechanism is forced, or ejected, from its coupled state between the pin housing and the lifter body. When such an ejection occurs, the valve spring propels the valve toward the valve seat while simultaneously propelling the lifter pin housing toward the lifter cam-following roller. In a typical deactivating valve lifter, the roller surface is crowned so that only a central region of the crown makes rolling contact with the mating cam lobe. The margins of the roller outside of the central region do not make contact with the mating cam roller.
In prior art deactivating hydraulic valve lifters such as disclosed in U.S. Pat. Nos. 6,497,207 and 6,814,040, if ejection occurs from a high lift position of the valve, the pin housing may actually strike the central region of the roller's crowned surface. Such contact of the roller by the pin housing can cause wear and damage (e.g., material spalling, pitting, debris brinelling) to the central region of the crown. Since the central region of the roller's crown runs against a mating surface of the engine's camshaft lobe, damage to the roller may be transferred to the mating camshaft lobe as well; and, since the camshaft is difficult to examine except by a complete engine teardown, costly repairs may result. Hence, it is important to prevent such damage to the central region of the roller's crown.
It is a principal object of the present invention to provide an improved valve-deactivation hydraulic lifter wherein the pin housing is incapable of striking the central region of the crowned surface of the lifter roller that makes contact with the associated cam lobe as a result of a latch ejection.
It is a further object of the invention to prevent damage to an engine camshaft lobe as a result of a latch ejection of a deactivation lifter.